(1) Field of the Invention
The invention relates to mountings for fine wire thermocouples and is directed more particularly to a mounting for use with thermocouples subject to detonation of high explosives, the mounting serving to shield the thermocouple from shock waves and from impaction by solid fragments and particles.
(2) Description of the Prior Art
The U.S. Department of Defense conducts experiments in which high temperature environments are produced by detonation of high explosives inside structures. It is often necessary to obtain a temperature history of the environment subjected to the explosive generated high temperature.
Thermocouples are typically used to measure the thermal transients produced by these experiments, in view of their simple operation and accuracy. However, thermocouple response time is directly related to the thickness of the sensing element used; i.e., the thinner the thermocouple element, the faster the response time. Fine-wire thermocouples (0.5 mil diameter) are often required to provide the necessary response time to fully capture the temperature transients of interest. Such fine-wire thermocouples are easily damaged or destroyed by airborne particles and fragments or strong air shock waves which accompany explosions. Since most fragments and the air shock occur prior to development of peak temperatures, unprotected thermocouples usually produce no useful temperature data from explosions.
Fine-wire thermocouples are often fielded in protective mounts which are designed to deflect particles and fragments from directly impacting the thermocouple element, but provide little or no protection from indirect particle impacts or air shock waves. Consequently, these protective techniques somewhat enhance measurement duration but often do not greatly improve long-term thermocouple survivability or reusability. Overall, these mounts increase useful data return from near zero for unprotected thermocouples, to approximately 50 percent.
Another currently used mounting technique shields a thermocouple from fragments and air shock by completely concealing the thermocouple, which is spring loaded, behind a protective cover until the air shock pressure pulse has decayed below a predetermined level, at which time the spring-loaded thermocouple pushes the cover away and pops out into the atmosphere. This method has several disadvantages. First, the spring-loaded thermocouple may not push the cover off because of mechanical failure. Second, even if the mount performs as designed, the time at which the thermocouple arrives at its final location is unknown and the early-time atmospheric temperature is not measured. Also, internal detonations typically feature numerous air shock reflections from the walls, ceiling, and floor, any of which may destroy an exposed fine-wire thermocouple. Small debris and particulate matter tend to remain airborne for prolonged periods and pose a significant hazard to fine-wire thermocouples. Based upon a small number of uses, data returned for this design is approximately 50 percent.
Accordingly, there remains a need for a thermocouple assembly including a fine-wire thermocouple which is shielded from shock waves and debris and which is able to provide a full temperature history of the atmosphere subject to the explosion, and which has enhanced survivability.